Some additional info:

I'm running Jenkins on an Amazon EC2 Instance, behind an Elastic Load Balancer with an SSL certificate.
Requests are routed to Jenkins through the following path:

Browser --> ELB (handles SSL) --> EC2 Instance (port 80)

In the browser's console, I see mixed content errors like:

Mixed Content: The page at 'https://......com/job/......./batchTasks/task/Deploy%20to%20Elasticbeanstalk/' was loaded over HTTPS, but requested an insecure resource 'http://updates.jenkins-ci.org/updates/hudson.tasks.Maven.MavenInstaller.json.html?id=hudson.tasks.Maven.MavenInstaller&version=1.609.1'. This request has been blocked; the content must be served over HTTPS.

Is there a warning on the /manage page that your reverse proxy configuration is broken? If so, fix it. This should take care of the warning you're seeing.

Yes, I can see that error in the /manage page.
However, the AWS ELB doesn't support rewriting responses. Therefore, there is no simple fix to this issue.

Since this setup is extremely popular, and AWS is likely the world leader in Cloud Computing, I think that a Jenkins-only solution should be implemented.
Perhaps a configuration to tell Jenkins to always generate HTTPS links in its pages.

In addition, every other page in Jenkins seems to work perfectly under my current setup. The problem seems to be only in the batch task plugin.

Moreover, the AWS ELB adds an X-Forwarded-Proto header to every request. Thus, Jenkins could use it to known which protocol to use when generating URLs for the browser.

Please consider my last comments before closing the issue.

The issue as originally reported is a duplicate and the warning you're seeing likely unrelated. Please file a separate enhancement request for the reverse proxy error in your environment.